1. Field of the Invention
The present invention relates to a method and system for monitoring the operating conditions of a tyre fitted on a vehicle.
The present invention relates to the possibility of carrying out actions, whether automatic or actuated or commanded by the driver, on the vehicle driving and/or control system to modify the vehicle""s behaviour according to measurements made on the tyre or on the wheel.
2. Description of the Related Art
Devices for measuring characteristic parameters such as pressure and temperature in a tyre are known from the prior art.
Patent application EP 887.211 describes a tyre monitoring system comprising a sensor, located inside the tyre, which is enabled to create an electrical pulse when the said sensor passes through the footprint area formed by the contact of the tyre with the ground during rotation. The system according to this patent also comprises means for measuring the ratio of the duration of the said electrical pulse to the duration of a revolution of the tyre and means for transmitting the said ratio to a processing unit within the vehicle.
In particular, the sensor is located inside the tread of the tyre, in such a way that the said electrical pulse has a first peak at the point where it enters the footprint area and a second peak at the point where it leaves the footprint area.
According to the teaching of this patent, the ratio of the time elapsed between the two peaks to the time taken for a complete revolution of the tyre can be used to discover the degree of flattening of the tyre during the operation of the vehicle.
This is because the sensor detects the instant of entry into the footprint area and the instant of exit from this area. It is thus possible to measure the length of this area, if the angular velocity of the tyre and its radius are known. The length of the footprint area is then related to the flattening of the tyre, which is a critical parameter of the tyre in use, particularly in tyres for heavy motor vehicles.
Patent application EP 0,689,950 describes a different method for monitoring parameters of a tyre, such as its pressure and temperature. In particular, a self-powered programmable electronic device located on the inner surface of a tyre or on its fitting rim is used. This device can be used to monitor and store the pressure, the temperature and the number of rotations of the tyre, and may comprise an extensometer, whose output signal measures the flexion of the inner surface of the tread strip, or an accelerometer which measures the intensity of the acceleration to which the tread strip is subjected. Additionally, the device is activated by an external signal at radio frequencies and transmits an alarm signal if a predetermined limit of the measured values is exceeded.
There are also known methods for measuring deformations of the tread strip of a tyre during movement and transmitting it to a receiver located on the vehicle.
Patent application WO 93.25400 describes a sensor located within the tread strip of a tyre and capable of transmitting a signal directly dependent on the aforesaid deformations, comprising a resonant circuit which oscillates at a predetermined characteristic frequency This resonant frequency is affected by the deformations of the tread strip during movement, and the sensor transmits electromagnetic waves proportional to these variations of the resonant frequency. These electromagnetic waves are received by a processing unit connected to a receiver located inside the vehicle.
U.S. Pat. No. 5,247,831 describes a method for monitoring the behaviour of the footprint area of a tyre during the operation of the vehicle to optimize the driving of the vehicle. In particular, a piezoelectric sensor consisting of longitudinal strips of piezoresistive rubber is inserted into the tread strip. This sensor is capable of measuring the deformations of the tread strip, since these strips change their electrical resistance as a function of the said deformations.
There are also known methods and devices for acting on the vehicle driving and/or control system, particularly on the devices which control the suspension systems of the vehicle, to control its behaviour according to the information obtained from the axles of the vehicle or from the hubs of the wheels.
The publication xe2x80x9cA method for the evaluation of the lateral stability of vehicles and tiresxe2x80x9d by the Società Pneumatici Pirelli S.p.A., presented at the xe2x80x9cInternational Automobile Tire Conferencexe2x80x9d at Toronto, Canada, on Oct. 22, 1974, illustrates a method of measuring the dynamic behaviour of the vehicle as a function of the forces developed by the various types of tyre set-up and the various conditions of the road surface.
The publication primarily refers to three forces which determine the dynamic behaviour of a tyre, specifically the vertical force, the longitudinal force and the lateral force.
The vertical force is that due to the dynamic load to which the tyre is subjected. The longitudinal force is that due to the torque applied to the axis of the tyre as a result of an acceleration or braking of the vehicle. The lateral force is the resultant of the force due to the characteristic angles of the suspension systems of the vehicle (camber and toe-in) and to the angular thrust (ply-steer) developed by the layers of inclined cords of the ply structure of the tyre, which are also present in normal operating conditions in straight-line motion, and of the thrust generated by the centrifugal force in drifting conditions. The sum of the forces developed by the four tyres generates a resultant system applied to the centre of gravity of the vehicle, which balances the inertial actions and determines the attitude of the vehicle as a function of the characteristics of the suspension systems of each axle. This resultant system is measured by suitable accelerometers, one of which is located on the front axle and one on the rear axle of the vehicle. The article includes a series of graphs showing the centripetal acceleration or the centripetal force applied to the centre of gravity of the vehicle as a function of the angle of skid of the corresponding axle. The graphs plotted for various ground conditions and with various types of tyres can be used to find the behaviour of the vehicle provided with a predetermined tyre set-up and to determine any lateral skidding in either the front or the rear axle in cornering.
U.S. Pat. No. 5,087,072 illustrates a system of what is called active suspension, consisting of four cylinders, one being provided for each wheel between the vehicle body and the hub of the wheel. These cylinders are powered by a hydraulic system operated by an electronic control unit. The system comprises a set of sensors for measuring the height of the vehicle above the ground for each suspension unit, and for making this measurement available to the electronic suspension control unit. The control unit operates the active cylinders separately according to the measurement of these heights.
The Applicant has observed that the aforesaid known systems of controlling the behaviour of a vehicle are based on systems of forces measured at the hubs of the wheels, and the systems of measuring the deformations of the tyre are based on the measurement of the deformations undergone by the tread strip in the footprint area of the tyre.
The Applicant has observed that the values measured in the cited art cannot be related in a unique way to the operating conditions of a tyre and, more precisely, to the system of forces developed by a tyre in each operating condition.
The present invention arises from the Applicant""s realization that the measurement of deformations of the tread strip, particularly in the footprint area of a tyre, cannot be used to identify the system of forces developed by the tyre and the deformations of the casing of the tyre connected to it and representative of the behaviour of the tyre. This behaviour is of considerable importance, especially during certain special events, such as braking or acceleration of the vehicle, drifting conditions, and variations of load on the tyre.
In accordance with the above, the present invention arises from the Applicant""s realization that the measurement of the deformations of the casing, since these are related in a unique way to the system of forces developed by the tyre in use, enables appropriate corrective actions to be taken on the vehicle drive and/or control system by means of the comparison of the said measured deformations with predetermined values thereof.
More specifically, the present invention relates to the control of the behaviour of a vehicle in motion by means of the measurement of characteristic deformations of the tyre during the movement of the vehicle, in such a way as to determine the operating conditions of the tyre by comparison with predetermined values representing the behaviour of the tyre in the various predicted states of deformation. According to the invention, the result of this comparison is used to generate a signal corresponding to a predetermined, preferably automatic, response of one or more devices controlling at least a mechanism for controlling the behaviour, including attitude, of the vehicle in motion, to keep the aforesaid behaviour of the vehicle within the limits of a predetermined behaviour, or to bring it back within these limits.
The Applicant has realized that, simply by knowing with certainty the behaviour of each tyre, in other words the function which relates the force developed by the tyre to its deformation, it is possible to act in the aforementioned way on the control devices of the vehicle in order to modify its behaviour, including attitude, in an optimal way.
It has been found that the measurements of the deformation of the casing structure of the tyre, at a given inflation pressure, in a triad of Cartesian coordinates, in other words, the deformation in the vertical direction, the deformation in the transverse direction and the deformation in the longitudinal direction, correspond in a unique or at least a reproducible way to the corresponding vertical, lateral and longitudinal forces which act on the tyre (or, in other words, to the forces which the tyre exchanges with the ground).
The Applicant has found that these deformations can be measured from the interior of the tyre independently of the events in the footprint area or, more generally, the interface conditions between the tyre and the ground.
It has also been found that the said predetermined values representing the behaviour of the tyre in the various predicted states of deformation can advantageously be:
calculated by simulation in a computer,
measured in the laboratory by means of special test machines which can be used to plot force-deformation graphs in various conditions,
obtained for each tyre on the vehicle in use or on a simulator apparatus.
In a first aspect, the present invention relates to a method for controlling the movement of a vehicle including at least one wheel provided with a tyre, the said method comprising the steps of:
determining the deformations of the said tyre by measuring them by means of the reflection of a signal emitted inside the wheel;
providing a database containing values of deformation of the tyre which correspond to a predetermined behaviour of the wheel;
comparing the said measured deformations with the said predetermined values of deformation; and
emitting a signal dependent on the result of the said comparison, to be used for controlling the behaviour of the vehicle.
In particular, the aforesaid method is implemented by means of the following steps:
measuring the extent of the characteristic deformations of the casing profile of at least one tyre fitted on the vehicle, at a given inflation pressure;
comparing the values of these characteristic deformations with stored values representing the behaviour of the tyre in the measured state of deformation; and
generating a signal for acting on at least one device regulating at least one mechanism for controlling the behaviour, including attitude, of the said vehicle in motion, corresponding to the action to be taken on the said mechanism to keep the said behaviour of the vehicle within the limits of a predetermined behaviour or to bring it back within these limits.
In a different aspect, the present invention relates to a system for controlling the behaviour of a vehicle in motion, comprising:
at least one unit for measuring at least one quantity correlated with a force transmitted to the ground by a tyre of the said vehicle;
a database comprising predetermined values representing the behaviour of the said tyre in relation to the said force; and
a data processing unit communicating with the said at least one measuring unit, capable of comparing the values of this quantity with the said values of the said database, and of emitting a signal to be used for controlling the behaviour of the vehicle.
The said signal may be an alarm signal or a signal for controlling a mechanism controlling the behaviour, including attitude, of the said vehicle to keep the said behaviour of the vehicle within the limits of a predetermined behaviour or to bring it back within these limits.
Preferably, the said signal acts on a device regulating the said control mechanism.
Preferably, the measuring unit is capable of measuring the rotation velocity of the tyre and/or its inflation pressure.
In a preferred embodiment of the system according to the invention, the aforesaid measuring unit comprises at least one sensor inserted into the supporting rim of the tyre and also, if necessary, a reflecting element located on the inner surface of the said tyre.
In a particular aspect of the invention, the quantity measured is the deformation of the casing profile of the tyre in a predetermined direction, preferably selected from the radial direction, the transverse direction and the circumferential direction.
In a further aspect, the present invention relates to a pneumatic wheel for vehicles, comprising:
a supporting rim which can be associated with a hub of the vehicle;
a tyre fitted on the said rim, comprising a casing structure provided with a crown portion extending axially between a pair of axially-opposed sidewalls, terminating in beads for joining the said tyre to the corresponding supporting rim, the said casing being provided with at least one reinforcing ply, having terminal flaps engaged with corresponding annular reinforcing structures embedded in the said beads, which forms a toroidal profile of the said casing;
an emitter of a signal which is to be reflected within the said tyre; and
a receiver of the said signal for the measurement of a quantity correlated with a force transmitted to the ground by the said tyre.
In a preferred embodiment of the wheel, the emitter and the receiver are integrated into a single sensor.
Even more preferably, this wheel comprises at least one unit for transmitting the aforesaid measurement to a data processing unit external to the said wheel.